Glossary

P10The value for which there is at least a 10% probability thatthe quantities actually recovered will equal or exceed thatvalue.

P50The value for which there is at least a 50% probability thatthe quantities actually recovered will equal or exceed thatvalue.

P90 The value for which there is at least a 90% probability thatthe quantities actually recovered will equal or exceed that value.

PACKERA seal used to isolate a section of a well, eg for testing or production from one of several formations. Packers are also used in operations such a cementing and acidising.

PAY, PAY SAND, OR PAY SECTIONProducing formation, or that formation which represents the objective of drilling.

PAY ZONE/HORIZONA formation containing producible hydrocarbons.

PERFORATE To pierce holes through well casing within an oil or gas-bearing formation by means of a perforating gun lowered down the hole and fired electrically from the surface. The perforations permit production from a formation which has been cased off.

PERFORATION/PERFORATING GUNHoles punched in the casing of a well at the pay zone to be produced, to allow oil or gas to enter the well. A Perforating Gun is a cylindrical tool loaded with explosive charges which are triggered opposite the pay zone, perforating the casing in many places.

PERMEABILITYThe degree to which a body of rock will permit a fluid to flow through it. It is a function of the shape of the capillary pore spaces and the degree to which pores are connected.

PETROLOGYThe study of rocks, their origin, chemical and physical properties and distribution.

PINCH OUTThe thinning out and disappearance over a distance of a formation, eg an oil bearing sandstone between layers of impermeable rock.

PIPE RACKWhere stands of drill pipe are stacked vertically in a derrick ready for use. Racks or frames are also sometimes used to store tubulars horizontally in yards and or offshore decks, and when transporting them offshore.

PIPE RAMSHydraulic rams in a blowout preventer which are shaped to fit around the drill-stem and seal the annulus. Blind Rams are designed in extreme emergency to shear through the drill pipe and seal the well completely.

PLUG/PLUG AND ABANDONTo seal a well, or part of a well with cement, e.g. before producing from a higher formation, sidetracking, or leaving the well permanently sealed and abandoned.

POOLAn Oil Pool is a reservoir or group of reservoirs sharing a common pressure system.

POROSITYThe volume of free space between the grains of a rock capable of holding fluid, (gas or liquid). It is expressed as a percentage of total gross rock volume.

PRESSURE BOMBA down hole pressure recording capsule used in well monitoring.

PROBABLE RESERVES Those unproved reserves which analysis of geological and engineering data suggests are more likely than not to be recoverable. In this context, when probabilistic methods areused, there should be at least a 50% probability that the quantities actually recovered will equal or exceed the sum of estimated Proved plus Probable Reserves. When probabilistic methods are used this corresponds to P50 value.

PRODUCIBLE LEASEA lease where one well or several wells have discovered hydrocarbons in paying quantities, but for which there is no production during the reporting period.

PRODUCIBLE ZONE COMPLETION The interval in a wellbore that has been mechanically prepared to produce oil, gas, or sulphur. There can be more than one zone completed for production in a wellbore.

PRODUCING LEASE A lease that is producing oil, gas, or sulphur in quantities sufficient to generate royalties.

PRODUCTION The operation of bringing the well fluids to the surface and separating them, and storing, gauging, and otherwise preparing product for the pipeline. Also refers to the amount of oil or gas produced over a given period

PRODUCTION CASING STRINGThe innermost steel lining of a well cemented in place and perforated for production in the pay zone. Note that production tubing is inserted inside this casing.

PRODUCTION TESTINGA production test concerns the capability to produce (productivity) of a well and its effects on the reservoir produced. A production test may continue for several months where extensive data is necessary prior to final commitment to development expenditures etc.

PRODUCTION TUBING STRINGThe string of pipe installed inside the casing of a production well, to a point just above the reservoir through which the fluids are produced. It may be 2" to 5" diameter or more, depending on the production flow and pressures anticipated.

PRODUCTION WELL/PRODUCERA development well specifically for the extraction of reservoir fluids.

PRODUCTION WELLHEAD AND TREEThe assembly of casing head, tubing head, connections and well-control valves fitted to a producing well. The "Christmas Tree" is the name given the complete assembly of valves, connecting flanges etc.

PRODUCTIVITY/PRODUCTIVITY INDEXThe continuous productive capacity of a well. The Index is measured as volume produced (e.g. barrels per day) divided by the drop in pressure (p.s.i.) to achieve that flow rate starting with a "shut in" pressure.

PROSPECTIVE RESOURCESThose quantities of petroleum which are estimated on a given date, to be potentially recoverable from undiscovered accumulations.

PROVED RESERVES Those quantities of oil and gas which, by analysis of geological and engineering data, can be estimated with reasonable certainty to be commercially recoverable, from a given date forward, from known reservoirs and under current economic conditions, operating methods and government regulations. When probabilistic methods are used this corresponds to the P90 value.

PULLING OUTRetrieving and stacking the drill-string on reaching target depth.

PUP JOINTA joint of pipe of non-standard length, to make up a string of tubulars to an exact required total length.

RATHOLEA hole in the drilling floor in which the kelly joint is kept when not in use.

RECOVERABLE OIL An estimated measure of the total amount of oil which could be brought to the surface from a given reservoir.

RECOVERY FACTORThe ratio between the volumes of oil and /or gas produced and produceable from a reservoir and the oil and/or gas originally in place.

RE ENTRYInserting the drilling, testing or logging string etc. into the wellhead.

RESERVES/RECOVERABLE RESERVESOil or gas that it is anticipated can be produced. Technical Reserves are theoretically producible at a gross operating margin by e.g. normal primary or secondary recovery methods, while Commercial Reserves are restricted to volumes recoverable at an acceptable profitability. The detailed definitions are important in oil and gas financial and other information.

RESERVOIRA porous, fractured or cavitied rock formation with a geological seal forming a trap for producible hydrocarbons. A common exploration maxim is that a prospective target must possess a related Source rock, Structure and Seal.

RESERVOIR PRESSUREThe pressure at reservoir depth in a shut-in well.

REWORKING A WELLMaintenance work on a well to stimulate production. This may involve cleaning out silt deposits etc., or stimulation techniques such as fracturing or acidising.

RIGA collective term to describe the permanent equipment needed to drill a well. It has come to include the onshore and offshore vehicles, mobile platforms, or vessels on which the equipment is installed.

RIGGING UP Act of getting a rig assembled and ready to start drilling.

ROLLER BITA rotary drilling bit which penetrates by pulverising the rock with its toothed wheels.

ROTARY DRILLING Method of drilling in which the drill pipe is rotated in order to rotate a bit.

ROTARY TABLEThe heavy turntable at the centre of a drilling-rig floor, which is rotated by the main rig power supply, and in turn rotated by the kelly.

ROUND TRIPRecovering the drill string from the bottom of the well to the surface and returning it to continue drilling. This may be e.g. to replace the bit. "Tripping" is arduous and interrupts "making hole".

SEALSee Reservoir. An impermeable fault or stratum of rock beneath or behind which hydrocarbons can accumulate.

SECONDARY POROSITYPorosity developed after the original deposition of a formation, for instance by the action of water on soluble components of the rock or well stimulation techniques.

SEISMIC ACQUISITION (2-D, 3-D, 4-D) Seismic data are used to map subsurface formations. A 2-D survey reveals a cross section of the subsurface. In a 3-D survey, seismic data are collected in the inline and crossline directions to create a three-dimensional image of the subsurface. In a 4-D or time-lapse 3-D survey, 3-D surveys are repeated over time to track fluid movement in the reservoir.

SEPARATORA process vessel used to separate gases and various liquids in a hydrocarbon stream. A Wellhead Separator is the first process vessel in a production operation, operating at or near wellhead pressures.

SET CASINGInstallation of steel pipe or casing in a well bore, normally cemented in place by surrounding it with a wall of cement.

SHOEThe strengthened fitting on the lower end of a string of casing to protect the tubulars and help direct the cement to the annulus.

SHOWEvidence of hydrocarbons in a formation such as fluorescence in cuttings or gas in the mud returning from down hole.

SHUT-IT PRESSUREThe pressure in a shut-in well; static pressure.

SIDE-TRACK/SIDE-TRACKED WELLA well re-drilled from an intermediate depth. Wells are re-directed or sidetracked for various reasons, but usually because of technical problems deeper in the original well.

SIDEWALL CORINGObtaining rock samples from the sides of a well bore using a special tool.

SOLUTION GASSee Associated Gas

SPACING The distance between wells producing from the same reservoir. Spacing is often expressed in terms of acres, e.g., 40-acre spacing, and is often established by regulatory agencies.

SPUDTo start drilling a new well (or re-start)

SQUEEZEInserting cement under pressure into the poorly sealed annulus of a well, past the existing material.

STAND OF PIPEA short length of drill pipe pre-assembled to save time in operations and stored vertically in the derrick ready for use, usually in lengths of three joints.

STEP-OUT WELL Well drilled adjacent or near to proven well to ascertain the limits of the reservoir.

STICKINGJamming of the drill string in the well borehole caused by usually a high differential pressure and a build-up of mud solids on the rock face.

STRADDLE PACKERA rubber packer or seal isolating a section of a well for production testing of the formation in question.

STRATIGRAPHIC TRAP Subsurface formation created by sedimentation that might trap an accumulation of oil and/or gas.

STRINGSee Joint, Drill-string, Casing, etc. Any number of connected joints of tubulars run in the well.

STRUCTUREA geological formation which, if sealed against leakage, could be a potential structural or stratigraphic trap or hydrocarbons. A man-made load-bearing construction, such as an offshore platform, usually designed by structural engineers.

STUCK PIPEDrill pipe, casing, or tubing that cannot be worked in or out of the hole as desired.

SURFACE CASING First string of casing set in well.

SUSPENDED WELLA well, usually a successful discovery well which is left temporarily sealed or plugged to be re-entered for further testing or for production purposes.

SWABBINGOperation using a swab to bring well fluids to the surface when the well does not flow naturally.